Electromagnetic traction increasing assembly

ABSTRACT

In railway transportation facilities and the like having a rail track system and a running system running on the rail track by means of running wheels, a system for increasing the axle load having a plurality of magnetic poles disposed in one of the two systems for producing magnetic flux, and a magnetic material disposed in the other system for producing an attractive force between the two systems by the action of the magnetic flux and a braking effort by the transfer movement of the magnetic flux, wherein the magnetic poles are energized within a speed range in which the product of the attractive force and the coefficient of adhesion is greater than the braking effort.

United States Patent 15] 3,653,329 Sasaki et al. [4 1 Apr. 4, 1972 [s41ELECTROMAGNETIC TRACTION 539,542 5/1895 Purvis ..105/77 INCREASINGASSEMBLY 2,198,928 4/1940 Wehner 3,307,058 2/1967 Kucera 105/77 X [72]Inventors: Akio Sasaki; Hiroshi Sakata; Nobuyoshi Tsuboi, of KalsutwshiJapan Primary ExaminerArthur L. La Point L H k Assistant Examiner-HowardBeltran [73 1 Assgnee td Japan Attorney-Craig,Antonel1i& Hill [22]Filed: Sept. 18, 1969 21 App1.No.: 858,949 [57] ABSTRACT In railwaytransportation facilities and the like having a rail track system and arunning system running on the rail track by [30] Foreign ApphcanonPriority Data means of running wheels, a system for increasing the axleload Sept. 20, 1968 Japan ..'....43/67612 having a plurality of magneticpoles disposed in one of the two systems for producing magnetic flux,and a magnetic material [52] U.S. Cl ..105/77, 105/ 184, 188/165,disposed in the other system for producing an attractive force 303/21CE, 303/21 CF, 310/93, 310/95 between the two systems by the action ofthe magnetic flux [5| Int. Cl ..B6lc 15/04, H02k 49/04, H02p 15/00 and abraking effort by the transfer movement of the magnetic ['58] Field ofSearch ..105/77, 78, 76, 184; 188/165; flux, wherein the magnetic polesare energized within a speed 5 246/D1G. 9, DlG. 10; 303/3; 310/93, 95range in which the product of the attractive force and the coefficientof adhesion is greater than the braking effort. [56] References Cited 3Claims, 8 Drawing Figures PATENTEDAPR 4 I972 33, 653 329 SHEET 1 OF 3BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a system for improving the adhesive performance by increasingthe axle load of the driving wheels of railway rolling stock and thelike.

2. Description of the Prior Art Employment of an intermediate truckrepresents one of the means adopted heretofore for the improvement ofthe adhesive performance of locomotives and the like. According to thismethod, a truck which does not contribute to the tractive effort of alocomotive or the like is fitted to a substantially central portion ofthe car body by means of air springs. In starting the locomotive, air isexhausted from the air springs and the body weight is substantiallyborne by the driving wheels so as to thereby augment the axle load ofthe driving wheels and increase the adhesive effort.

According to one of prior art examples, the axle load of the drivingwheels at the time of starting is set at 16.8 tons per axle. Afterstarting, air pressure fed into the air springs is gradually increased.This increases the share of the body weight by the intermediate truckand the axle load of the driving wheels is reduced to a normal workingvalue of 16.0 tons per axle.

According to the means described above, a truck which does notcontribute to the tractive effort must be provided in addition to thedriving trucks, and yet there is a limitation to the maximum value ofthe axle load obtained at the driving wheels. This limit is determinedprimarily by the body weight. Accordingly, a heavy body weight isrequired when a large axle load is required. It is disadvantageous thatthese weights should be entirely imparted to the rails.

Various resolutions for these problems were suggested so as to increasethe maximum adhesive effort by means of the attractive force exertedbetween an electromagnet and the rail. However, no success could beobtained for a practical application from these suggestions, even thoughvarious designs and structures were tried on the basis of thesesuggestions.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a system capable of increasing the axle load without in any wayimposing a heavy burden upon the rails.

Another object of the present invention is to provide a system capableof obtaining an axle load as desired which is more than that determinedby the body weight.

The present invention is essentially featured by the fact that a forceof attraction is produced between the rail track system and the runningsystem of railway rolling stock or the like, and more particularly, bygenerating the-force of attraction merely within a predetermined speedrange.

Other objects, features and advantages of the present invention will beapparent from the following detailed description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view forillustrating the basic principle of the present invention and includes aschematic connection diagram showing the control circuit of theembodiment shown in FIGS. 4a and 4b,-

FIG. 2 is a graph for showing typical speed characteristics of thesystem shown in FIG. 1

FIG. 3 is a graph showing the data from an experiment performed on thebasis of the basic principle shown in FIGS. 1 and 2;

FIG. 4a is an elevational view of an embodiment of the system inaccordance with the present invention;

FIG. 4b is a plan view of the embodiment shown in FIG. 4a;

FIG. 5 is a graph illustrating the operating principle of the systemshown in FIGS. 4a and 4b;

FIG. 6a is a graph showing one example of an actual measured coefficientof adhesion in relation to speed; and

FIG. 6b is a graph showing the experimental speed characteristics of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a core 10having a plurality of magnetic poles 10a, 10b, 10c and 10d is disposedopposite to a magnetic material 12 in such a manner as to define a verysmall air gap therebetween. An excitation coil is wound around each ofthe magnetic poles 10a, 10b, 10c and 10d. It is commonly known that,when such excitation coils are energized by a DC source 14, magneticflux is produced as shown by the dotted lines and an attractive force Wattracting the core 10 and the magnetic material 12 toward each other isproduced between the core 10 and the magnetic material 12.

On the other hand, when the core 10 is moved in the direction of thearrow, the magnetic flux is transferred and an eddy current is generatedin the magnetic material 12. Due to the mutual action between the eddycurrent and the magnetic flux, a force directed in a direction toobstruct the movement of the core 10 is produced in the core 10, thatis, a braking effort B is produced in the core 10. This arrangement iscalled an eddy current brake. Alternatively, the core 10 may be heldstationary and the magnetic material 12 may be moved to similarlyproduce an eddy current braking effort since the braking effort isproduced by the relative movement between the core 10 and the magneticmaterial 12.

The attractive force W and braking effort B acting between the core 10and the magnetic material 12 vary relative to the speed of movement in amanner as shown in FIG. 2.

More precisely, the attractive force W decreases with an increase in thespeed and the braking effort B increases with an increase in the speed.The reason therefor will be briefly described hereunder. The eddycurrent generated in the magnetic material 12 by the movement of themagnetic flux increases with the increasing speed. Further, a countermagnetomotive force which will cancel the magnetic flux is produced inthe magnetic material 12 by the eddy current. Since an increase in theeddy current is followed by a corresponding increase in the countermagnetomotive force, the flux density in the air gap between the core 10and the magnetic material 12 decreases with an increase in the speed.Thus, the attractive force W decreases with an increase in the speed.

Further, the product of the braking effort B produced by the eddycurrent and the speed, that is, the energy consumed at that time isequal to the eddy current loss occurring in the rails. Accordingly,neglecting the saturation of the flux density in the rails, the eddycurrent loss described above is approximately proportional to the squareof the speed and hence the braking effort B increases with an increasein the speed.

Data of an experiment performed by the inventors will be shown by way ofexample. An apparatus used in the experiment had the followingspecifications:

Number of coils (number of poles) Number of turns per coil Data wereobtained in two cases, that is, a case in which 12 coils are dividedinto two coil assemblies each consisting of six coils to provide twopoles, and a case in which each of the 12 coils serves as a pole toprovide 12 poles.

In a stationary state of the apparatus, an 6,160 pounds (2,800 kg.) of 3l0 amperes is supplied to the excitation coils, while an attractiveforce of 4,4000 pounds (2,000 kg.) is produced when a current of amperesis supplied to the excitation coils. These attractive forces decreasewith an increase in the speed as shown by the one-dot chain lines W andW in FIG. 3. The attractive force is not influenced by the number ofpoles.

Regarding braking effort, there is a great variation between the brakingeffort in the case of two poles and that in the case of 12 poles. Thebraking efforts in the case of two poles are represented by the solidlines B and B while those in the case of 12 poles are represented by thedotted lines B, and B Where, B and B correspond to an excitation currentof 310 amperes, while B and B correspond to an excitation current of I50amperes.

FIGS. 4a and 4b show a preferred embodiment of the present inventionbased on the principle described above. A rigid frame 16 is providedwith axle boxes 20 and beams 22. The axle boxes 20 support drivingwheels 18 whose driving mechanism is not shown. The rigid frame 16 isconnected to a truck frame 26 through axle springs 24. The truck frame26 is connected to a car body (not shown) through bolster springs 28 anda center plate 30.

A set of electromagnetic devices 32 each comprising a core andexcitation coils are mounted on the beams 22. In this case, the magneticpoles of each electromagnetic device 32 must be opposite to a rail 34with a predetermined air gap defined therebetween. The excitation coilsare energized by a suitable power source. The armature current of thedriving motor may for example be utilized as the power source. This isadvantageous in that the axle load of the wheels I8 can be varieddepending on the torque produced by the driving motor in a manner aswill be described later.

Referring to FIG. 5, the operation of the apparatus shown in FIGS. 4aand 4b having a structure as described above will be described.

In a deenergized state of the electromagnetic devices 32, an axle load Wdue to the body weight is imparted to the wheels I8. w lJ. which is theproduct of the axle load W and coefficient of adhesion ,u. gives thelimit of adhesion at this specific instant. This is represented by theone-dot chain line in FIG. 5.

Then when the electromagnetic devices 32 are excited, an

attractive force is produced between them and the rails 34.

This force is transmitted to the axles through the beams 22, rigid frame16 and axle boxes with the result that the axle load of each axle isincreased by Wa. The increment Wa ofthe axle load multiplied by thecoefficient of adhesion ,u, that is Wap. can be utilized as adhesioneffort. This is represented by the thin solid line in FIG. 5. As iscommonly known, the coefficient of adhesion ,u. between the wheel I8 andthe rail 34 decreases with an increase in the speed of the wheel 18.

Here, it is supposed that a braking effort F 8 produced concurrentlybecomes equal to the adhesive effort Wan at a speed V Addition of theincrement Way. to the limit of adhesion Won gives (W, Wa)p. which isrepresented by the two-dot chain line in FIG. 5. The sum (Wo Wa),u. canbe utilized as an adhesive tractive effort during acceleration. However,the breaking effort F produced concurrently acts as a reverse componentagainst the effort (W0 W3)[.L. Accordingly, (W0 Wa),u. F,, can actuallybe utilized as the adhesive tractive effort. Thus, the apparatus shownin FIGS. 4a and 4b exhibits its marked effect in a range in which (W0Wa)p. F is greater than Wop, that is, in a speed range in which thespeed is lower than V,.

FIG. 6b shows an adhesive effort and braking effort relative to speed inthe apparatus shown in FIGS. 4a and 4b. In this case, however, it issupposed that the coefficient of adhesion ,u. varies in a manner asshown in FIG. 6a.

As seen from FIG. 6b, the adhesive effort F Wp.) becomes greater with anincrease in the excitation current, but the braking effort B producedconcurrently is also increased with the result that the speed at whichtheir magnitudes are equal to each other is gradually reduced. It willbe noted, however, that the adhesive effort which can be utilized at thetime of starting becomes greater with an increase in the excitationcurrent. Therefore, when the armature current of the driving motor isutilized to energize the excitation coils as previously described, thespeed at which the adhesive effort and braking effort become equal toeach other is raised since the armature current decreases with anincrease in the speed after starting.

It will thus be understood that the available speed range of theapparatus can be widened with an increase in the speed.

Further, as can be noted from the data shown in FIG. 3, the apparatusdescribed above can be utilized as a braking device. That is to say, thenumber of poles may be increased so as to positively utilize the brakingeffort. And, this is more effective at higher speeds.

The braking effort in a high speed range of the order of 62 miles perhour km.p.h. is considerably great when the electromagnetic device 32includes 12 poles. Therefore, means may be provided to switch over thenumber of poles of the electromagnetic device 32 in the apparatus sothat the apparatus can be operated as a means for increasing the axleload during starting and as a braking device during braking.

A circuit for accomplishing the above operation is shown in FIG. I, inwhich there is provided a tachometer generator TG for producing avoltage proportional to the wheel speed, a relay 2R having normallyclosed switches 20, Zbfand 2c, and a relay 4R having normally openedswitches 4a, 4b and 4c. The relay 2R is operative when the wheel speedis higher than a predetermined value within a speed range lower than thespeed V in FIG. 5, but the relay 4R is operative when the wheel speed ishigher than another predetermined value within a speed range higher thanthe speed V If a switch is closed when starting the wheel, the relays 2Rand 4R are not effected or operative since the wheel speed is lower thanthe predetermined value. Hence, the magnetic poles 10a and 10b are eachenergized with a current passed through from the upper terminal to thelower terminal thereof to produce magnetic flux in the same directionwith each other, while the magnetic poles 10c and 10d are each energizedwith the current passed through from the lower terminal to the upperterminal to produce magnetic flux in the same direction with each otherbut opposite to the magnetic poles 10a and 1011. Thus, the magneticpoles 10a, 10b, 10c and 10a act as a two-pole magnetic device and, as aresult, the brake effort produced is minimum at this state.

If the switch is closed when the wheel speed exceeds the predeterminedvalue, the relays 2R and 4R become operative, and the structures 4a, 4band 4c are closed while the switches 2a, 2b and 2c are opened.Consequently, the magnetic poles Illa and 100 produce magnetic flux inthe same direction with each other but opposite to that of the magneticpoles 10b and 10d. Thus, the magnetic poles 10a, 10b, 10c and 10d act asa four-pole magnetic device and, as a result, the braking effort becomeslarge at this state.

While a specific embodiment of the present invention has been describedin the above, it will be apparent for those skilled in the art that thepresent invention is in no way limited to such a specific embodiment,and various changes and modifications may be made therein withoutdeparting from the scope of the appended claims.

We claim:

I. In railway transportation facilities and the like having a rail tracksystem and a running system running on the rail track by means offunning wheels, a system for increasing the axle load comprising anelectromagnetic device disposed in one of said two systems for producingmagnetic flux, and a magnetic material disposed in the other said systemfor producing an attractive force between said two systems by the actionof said magnetic flux and a braking effort by the transfer movement ofsaid magnetic flux, the improvement comprising means for detecting thespeed of said running system, means for comparing the detected meanswith a predetermined speed, at which the product of the attractive forceproduced by said electromagnetic device and the coefficient of adhesionis greater than the braking effort produced concurrently, and means forenergizing said electromagnetic device when the speed of said runningsystem is lower than said predetermined speed.

2. A system for increasing the axle load as claimed in claim ll, furthercomprising means for changing the number of magnetic poles of saidelectromagnetic device, said changing 1 further comprising at least oneelectric motor for driving said running system, in which saidelectromagnetic device is disposed in said running system and saidmagnetic poles are energized by a current which is proportional to thecurrent of said electric motor.

1. In railway transportation facilities and the like having a rail track system and a running system running on the rail track by means of funning wheels, a system for increasing the axle load comprising an electromagnetic device disposed in one of said two systems for producing magnetic flux, and a magnetic material disposed in the other said system for producing an attractive force between said two systems by the action of said magnetic flux and a braking effort by the transfer movement of said magnetic flux, the improvement comprising means for detecting the speed of said running system, means for comparing the detected means with a predetermined speed, at which the product of the attractive force produced by said electromagnetic device and the coefficient of adhesion is greater than the braking effort produced concurrently, and means for energizing said electromagnetic device when the speed of said running system is lower than said predetermined speed.
 2. A system for increasing the axle load as claimed in claim 1, further comprising means for changing the number of magnetic poles of said electromagnetic device, said changing means including a first relay operated over a first predetermined speed and a second relay operated over a second predetermined speed higher than said first predetermined speed, the number of the magnetic poles being minimum when said first relay is operated and being maximum when said second relay is operated.
 3. A system for increasing the axle load as claimed in claim 1 further comprising at least one electric motor for driving said running system, in which said electromagnetic device is disposed in said running system and said magnetic poles are energized by a current which is proportional to the current of said electric motor. 